The present invention relates to latches or bolts used in doors. More particularly it relates to a particular type of door bolt used for bolting the inactive one of a pair of swinging double doors. More particularly the present invention relates to bolts mounted flush with the free edge of one of a pair of swinging double doors for bolting the inactive door to the door frame. Bolts of this type are referred to as flush bolts. In typical application, one or two flush bolts may be used in an installation. Typically one bolt is used to bolt the top of the inactive door to the ceiling or top of the door frame and one bolt is used to bolt the bottom of the inactive door to the floor or bottom of the door frame. Flush bolts may be manual, semi-automatic, or automatic. A manual flush bolt must be operated by hand in order to open or close the door. A hand-operated switch or lever controls the position of the bolt between an engaged position and a disengaged position. In a semi-automatic flush bolt, the door may close and latch itself automatically, but a hand-operated control lever or switch must be manually activated in order to release the bolt to open the door. In an automatic flush bolt, a trigger or sensor on the free edge of the inactive door senses whether or not the active door is closed, i.e. is adjacent to it. When the active door is closed, the trigger causes the automatic flush bolt to change to the engaged position, when the active door is again open, the trigger releases causing the automatic flush bolt to return to the disengaged position.
Although fit for their intended purposes, semi-automatic and automatic flush bolts of the prior art feature complicated structures and large numbers of parts. Typically two or more springs are necessary within the mechanism in order to achieve proper biasing of the various parts.